The present embodiments relate to adjusting a field distribution of an antenna arrangement of a magnetic resonance system.
In magnetic resonance (MR) systems, antenna arrangements may be used to generate a radio-frequency field (e.g., a B1 field). Such antenna arrangements may, for example, have a cylindrical or tubular structure arranged around a patient receiving bore of the magnetic resonance system. Examples of antenna arrangements (e.g., body coils) are described in the publications U.S. Pat. Nos. 8,362,775 B2, 6,781,378 B2, 8,072,218 B2, and US 20170016969 A1.
Alternatively, such an antenna arrangement may also be provided in conjunction with a local coil. The antenna arrangement may include an actual antenna (e.g., a birdcage antenna or a transverse electromagnetic (TEM) resonator (e.g., TEM antenna) and a radio-frequency (RF) screen in order to provide a defined environment for the field generation. The decisive factor for optimal operation of the antenna arrangement is the interaction between the antenna and the RF screen in order, for example, to achieve a symmetrical or homogeneous field distribution. Herein, the distance between the antenna and the RF screen is to be maintained as exactly as possible. However, practical implementations of such antenna arrangements are based on a mechanical separation of the antenna and RF screen and so adjustment elements are to be provided to compensate the tolerances present.
In addition to mechanical adjustment elements, adjustable capacitors (e.g., trim capacitors) may be provided in order to compensate these mechanical tolerances and to improve (e.g., homogenize) the field distribution or increase field symmetry. However, adjustments of this kind are very time consuming and hence costly. During operation of the magnetic resonance system, the homogeneous or symmetrical field distribution of the B1 field emitted by the antenna arrangement may also, for example, be influenced by the patient to be examined.